(1) At the end of the game, set three groups of * * * games as event M, and then set it in this game, where A wins as event A and A wins as event A, then p (m) = p (a+a) = p (a)+p (a) = 35× 35+25×12.

(ii) The possible values of ξ are 0, 1, 2, 3,

Then p (zeta p(ζ= 0)= 25,

P(ξ= 1)=35×25=625，

p(ξ= 2)=(35)2×25 = 18 125，

P(ξ=3)=(35)3=27 125，

The list of ∴ξdistribution is as follows:

Mathematical expectation of ξ 0 123p (ξ) 25625812527125 ξ e = 0× 25+1× 625+2×18/.